1. Technical Field
This invention relates generally to multi point measuring instruments, and more particularly to a measuring instrument having a plurality of probes disposed in a compact, easily maneuverable support member.
2. Background Art
Multi point measurement instruments are typically used to measure the contour of relatively small objects, such as teeth. For example, it is desirable to accurately identify the shape of a ground tooth prior to fitting a crown over the tooth. Also, it is often desirable to inspect relatively small articles of manufacture to assure correct three-dimensional alignment and relative tolerances of particular features of the article. U.S. Pat. No. 4,997,369 issued Mar. 5, 1991 to Aaron Shafir describes a probe that is movable along three independent axes. In order to obtain the plural measurements necessary to describe a surface contour, the probe must be moved after each independent measurement, the position data recorded, and the probe moved to the next position whereat the procedure is repeated. This process is cumbersome, time consuming and subject to error if the anchor point of the apparatus is inadvertently moved during the measurement process.
More recently, U.S. Pat. No. 5,257,184 was issued Oct. 26, 1993 to David Mushubac for a device capable of taking measurements which provide a cross-sectional outline of a human tooth. The Mushubac device uses a plurality of stylus elements, additional components for establishing a reference position, and various means for measuring the displacement of the styli along respective axes. The Mushubac instrument is very complex and requires considerable skill and training in order to assure accurate data measurements. Also, the large number of relatively fragile precision components make the instrument costly to manufacture and difficult to calibrate, repair and maintain.
In other surface contour measuring devices, spring-loaded levers are arranged in an arcuate pattern about the tooth and extend outwardly from the patient's mouth to a pivot point. The outward ends of the levers are connected to light-optic bundles or other measurement device, such as LVDTs or glass encoders, which track and amplify the displacement of the contact tip. It has been found that mechanical-linkage devices for measuring surface contours have a number of inherent problems. For example, each of the spring-loaded levers typically have a different angle of approach to the tooth surface which must be maintained from the contact point to the view, or measurement, plane of the device. The view, or measurement, plane is generally a mechanically amplified plane provided by the ends of levers opposite the contact end, providing an enlarged cross-sectional representation of the actual tooth surface. Each of the levers must wrap around the hand of the operator holding the device to provide a view plane behind the operator's hand. The direction of displacement at the probe end of the lever must be duplicated at the view plane, requiring that each lever have at least three pivotable segments which rotate about separate pivot points, and a requirement for interconnecting linkage between the segments. This arrangement makes it difficult to maintain accurate simultaneous translation of all of the segments of all of the levers, thereby affecting the accuracy of the measurements. Furthermore, mechanical-linkage measurement devices are cumbersome to use, prone to erroneous readings if not held steady during the measurement process, and may appear threatening to the patient on which the instruments are used.
Levers with pivots and fixed lengths form a rigid mechanical linkage between probe tips and measurement means wherein displacement errors can be induced through bending or twisting of the levers or misalignment of the pivot points. The hydraulic linkage cited here allows virtually any orientation between contact probe and measurement means with minimal error in displacement. In addition, the hydraulic linkage allows the displacement at the contact probe to be mechanically amplified at the measurement end, thereby producing a larger relative displacement which can be then measured more accurately. The radial arrangement of the probes in an arch format provides a means whereby the fixed reference point is carried with the assembly, eliminating the need for an external fixed reference.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a multi point measurement instrument for small articles such as teeth, that does not require fixed mechanical linkage between the contact probe and the measurement, or readout, components of the instrument. It is also desirable to have such an instrument that is compact, easy to use, and has a flexible linkage between the probe support and the measurement components of the instrument. It is also desirable to have such an instrument wherein the probe support and measurement components are separately replaceable and interchangeable with different probe support configurations and measurement devices.